ABSTRACT:

This paper explains the engineering Waste Injection (WI) assurance process and shows examples where its application successfully supports the development of major drilling projects where WI was a critical part of the operation. The methodology followed by the process gives the tools to manage responsible and safely a permanent disposal of the drilling waste while maintaining drilling pace and schedules. The process begins with a full feasibility study FEED where accurate geomechanical modeling is required to define the optimal operational conditions to achieve success during the injection, disposal formation, containment zones, capacity, and operational parameters are defined in the study. The next stage is the calibration of the model with a full injectivity test into the target formation. Once the injection operation begins, monitoring injection and decline pressures allows total control and verification of the injection parameters to maintain control of the waste disposal domain. Injection pressure analysis, during and post injection, determines how the fracture system is behaving as WI progresses. Recalculation of the main geomechanical formation parameters based on the formation pressure response needs to be conducted in order to obtain accurate forecast of the disposal domain and formation capacity. As conclusion, more than 28 MM bbls of waste have been successfully injected worldwide, reducing considerably the impact to the environment compared to conventional disposal options.

1. INTRODUCTION

Waste Injection, WI, operations were initiated at the end of the 80's decade, when reduced volumes of oily waste combined with drilled cuttings where injected into the subsurface through tubular or annulus spaces. Some of these operations could be considered just like pumping jobs without the understanding of the real injection process neither the behavior nor response of the disposal formation. These procedures lead, in some instances, to non productive time events such as well plugging, disposal fracture screen outs, elevated operational pressures above equipment capabilities and in few cases even to more dramatic environmental impacts due to contamination caused by injected waste breaking to protected zones, i.e. aquifers or reaching to the sea bed. These events caused liabilities that generated negative economical effects, forcing organizations to create an engineering program that analyzes the overall process and helps understanding the subsurface waste injection and all its implications. Initially this program focused on monitoring the injection operation and defining the operational procedures required to guarantee the injectivity into the subsurface, nowadays the program has evolved to a fully systematic engineering assessment tool that uses the hydraulic fracturing theory to define the subsurface behavior of the fracture system created while pumping the waste into the selected disposal formation, the process is recognized in the E&P industry as the WI assurance process.

2. WASTE INJECTION PROCESS

The search for new hydrocarbon resources has been pushing the exploration and drilling to new frontiers with extreme and sensitive conditions. Essentially WI was the response to the necessity of innovative technologies that allow E&P companies to drill in remote geographical areas under challenging conditions where traditional waste management techniques cannot be used.

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